add SEO enhancements: OG images, meta robots, FAQ block, image sitemap

- Per-page SEO controls: meta robots directives, focus keyword, OG image
- Site-wide default OG image in admin settings
- FAQ block type with FAQPage JSON-LD schema
- Enhanced Organization JSON-LD with business info, contact, address
- Image sitemap with product images
- SEO preview panel with Google/social card mockups
- SEO checklist with real-time scoring
- Business info section in site editor
- GSC integration scaffolding (OAuth, client, cache)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

lib/berrypod_web/components/layouts/shop_root.html.heex

@@ -11,6 +11,9 @@
           "Welcome to #{@site_name}"
       }
     />
+    <%= if assigns[:meta_robots] && assigns[:meta_robots] != "index, follow" do %>
+      <meta name="robots" content={assigns[:meta_robots]} />
+    <% end %>
     <!-- Favicon & PWA -->
     <link rel="icon" href="/favicon.svg" type="image/svg+xml" />
     <link rel="icon" href="/favicon-32x32.png" sizes="32x32" type="image/png" />